The entire disclosure of Japanese Patent Application No. 2001-33207 filed on Feb. 9, 2001 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to a sheet-fed printing press equipped with an inspection unit for checking the printing quality of a sheet-like material.
2. Description of the Related Art
Generally, a sheet-fed printing press is equipped with an inspection unit for checking the printing quality of a sheet (or sheet-like material) printed by a printing unit. In the inspection unit, a sheet being transported by a transport chain toward a pile board of a delivery unit after being printed by the printing unit is sucked onto a guide surface of a suction table. On the guide surface, the sheet is spread as uniformly as possible (so that it becomes substantially wrinkle/crease fuss), and the printed surface of the sheet is photographed by a picture taking device, such as a CCD camera. A control device compares signals from the picture taking device with prescribed quality standards. Sheets which meet the quality standards, and sheets which do not meet the quality standards are separated, and delivered onto predetermined pile boards (see, for example, Japanese Unexamined Patent Publication No. 5-254091).
The above-described sheet-fed printing press, however, has required that a clearance needs to be provided between the guide surface of the suction table and the front ends of gripper devices (chain gripper devices), which are supported by the transport chain to grip the sheet, in order that the gripper devices and the suction table will not interfere with each other during travel of the gripper devices.
As shown in FIGS. 4(a) and 4(b), a printed sheet W travels on a guide surface 101 of the suction table, with a leading edge Wa of the sheet W being gripped by a gripper 100a and a gripper pad 100b of a gripper device 100. If the sucking force of the suction table is weak when the sheet W is photographed with a CCD camera 102 of an inspection unit, the sheet W cannot be spread on (sucked by) the guide surface 101 of the suction table. As a result, the sheet makes an unstable motion, thereby affecting the picture taking of the CCD camera 102 of the inspection unit. To avoid this situation, the sucking force of the suction table needs to be increased in order to spread (suck) the sheet W reliably on (onto) the guide surface 101 of the suction table, as shown in FIGS. 4(a) and 4(b).
In taking a picture of the sheet W by the CCD camera 102 of the inspection unit while increasing the sucking force of the suction table, there is a distance between the gripper pad 100b and the guide surface 101, as stated earlier, and the sheet W is transported in a state as shown in FIG. 4(a) or 4(b), although the state of transport differs according to each sheet W. Assume that the sheet W is to be photographed by the CCD camera 102 in the state of FIG. 4(a). Compared with the sheet W transported in the state of FIG. 4(a), the sheet W transported in the state of FIG. 4(b) falls into a state such that a trailing edge Wb of the sheet W extends beyond a detection area E (i.e., the trailing edge Wb recedes). Thus, the sheet W may be judged to be a defective sheet, although it is a normal sheet. (A similar problem occurs in the opposite case, in which the trailing edge Wb enters the detection area E too much.) On the other hand, the leading edge Wa of the sheet W transported in the state of FIG. 4(a) is bent in the form of a crank (nearly at right angles), thus making sheet jogging poor at the delivery unit.
As a countermeasure, Japanese Unexamined Patent Publication No. 10-034891 proposes a technique which comprises: providing grooves, corresponding to the travel paths of the grippers, in the suction table; designing the transport path of the sheet, which is transported by the gripper devices (concretely, the transport path is at the same height as the height of the gripper pad of the gripper device), to be at nearly the same height as the guide surface of the suction table; and inserting the grippers of the gripper devices into the grooves to avoid the interference of the grippers with the suction table, while causing the entire surface of the sheet gripped by the gripper devices to be sucked onto and spread along the guide surface to prevent the instable motion of the sheet, thereby decreasing inspection errors.
With the sheet-fed printing press disclosed in Japanese Unexamined Patent Publication No. 10-034891, however, while the sheet is traveling on the guide surface of the suction table, the sheet is rubbed against the edges of the grooves and scratched thereby. Particularly in a perfecting press, the sheet is instantaneously turned into a wasted sheet. Moreover, the sheet is deformed into a corrugated shape because of the grooves discretely present in a sheet width direction. Thus, high accuracy inspection could not be performed.
The present invention has been proposed in consideration of the above-described circumstances. It is the object of the invention to provide a sheet-fed printing press capable of effectively suppressing behaviors of a leading edge of a sheet-like material gripped by gripper devices to make a highly accurate inspection.
According to the present invention, there is provided a sheet-fed printing press comprising:
a transport chain;
gripper devices supported by the transport chain and each having a gripper and a gripper pad for gripping a sheet-like material;
an inspection device for inspecting the sheet-like material gripped and transported by the gripper devices; and
a sheet-like material guide member having a guide surface for guiding the sheet-like material at a position of inspection by the inspection device, and a suction hole for spreading the sheet-like material along the guide surface, and wherein
an inclined portion, which gradually decreases a distance between the gripper pads and the guide surface from an upstream side toward a downstream side of the guide surface in a sheet-like material transport direction, is provided on the downstream side of the guide surface, and
groove portions, through which the grippers pass, are formed in the inclined portion.
According to this feature, behaviors of the leading edge of the sheet-like material gripped by the gripper devices can be suppressed effectively. Thus, inspection errors can be decreased to increase the accuracy of inspection. Moreover, the sheet-like material is minimally deformed, effectively preventing scratches and performing satisfactory sheet jogging.
In the sheet-fed printing press, a suction hole for spreading the sheet-like material along a guide surface of the inclined portion may be provided in the guide surface or groove portions of the inclined portion. Thus, the leading edge of the sheet-like material is further stabilized to increase the accuracy of inspection.
In the sheet-fed printing press, an inspection surface for inspection by the inspection device may comprise the guide surface of the sheet-like material guide member and the guide surface of the inclined portion.
In the sheet-fed printing press, the inclined portion may comprise strip-shaped portions disposed at predetermined intervals in a sheet width direction, and the predetermined intervals may define the groove portions.
In the sheet-fed printing press, the inclined portion may be supported by the guide surface of the sheet-like material guide member.
In the sheet-fed printing press, the transport chain may support a plurality of gripper devices.
In the sheet-fed printing press, the sheet-like material guide member may include a plurality of groove portions.